The stratigraphy of a Late Palaeozoic borehole section at Douglas River, eastern Tasmania: a synthesis of marine macro-invertebrate and palynological data

A section 236.8 m in thickness of Late Palaeozoic (Late Carboniferous-Permian) rocks of the Lower Parmeener Super-Group was encountered in a borehole at Douglas River, eastern Tasmania. Lithological, marine macro-invertebrate and palynological data are documented and collated. The section displays many similarities with sequences elsewhere in eastern and northeastern Tasmania, but is unusual in the development of rocks (including Tasmanites shale) as old as Early Tamarian. This occurrence may indicate a narrow, but significant east-west breaching of the land barrier which persisted throughout the Tamarian over most of eastern and northeastern Tasmania. Acritarch swarms coeval with sedimentation occur at intervals, whereas other acritarchs may be derived from earlier Palaeozoic rocks. The Tasmanian Late Permian palynofloras lack diversity and resemble those from the Transantarctic Mountains, Antarctica, rather than those from elsewhere in eastern Australia

River Clyde Environmental Change Network diatom analysis project final: report to SEPA

This report provides details of work performed on the SEPA contract to ENSIS Ltd. involving the preparation and analysis of historic (September 1994 – August 2010) Environmental Change Network diatom samples from the River Clyde at the Tidal Weir. Diatoms were collected from the site by SEPA, forwarded to ENSIS Ltd and prepared for analysis following protocols described in the United Kingdom Environmental Change Network’s “Protocols for Standard Measurements at Freshwater Sites” (Sykes et al., 1999). Samples were taken at the site at various times of year and a full list of those that have been received by ENSIS is provided in Appendix 1. For this project, in order to minimise any inter-seasonal variability in the time-series, Kate Arnold from SEPA selected a subset of 16 summer samples for analysis, all collected between late July and early September. Approximately 400 diatom valves were counted per sample by Gina Clarke using a light microscope with phase contrast at 1000x magnification. Count data were recorded on a spreadsheet and transferred to ENSIS where they have been added to the ECN diatom database and have also been provided to SEPA. The diatom count data was run through the DARLEQII program (Kelly et al, 2011) in order to generate Trophic Diatom Index (TDI), Ecological Quality Ratio (EQR) and status class values (high, good, moderate, poor, bad) for each sample. Alkalinity values for the calculations were provided by SEPA for all samples except the earliest three in the timeseries, for which the average from all samples was used. Both TDI3 and TDI4 scores were calculated for all samples and the scores reported here. Table 1 is taken from the DARLEQII user guide (Kelly et al, 2011) and describes the output fields provided in the results section for the site below. Electronic copies of the full DARLEQII program output have been provided to SEPA

Abstract Interpretation of Stateful Networks

Modern networks achieve robustness and scalability by maintaining states on their nodes. These nodes are referred to as middleboxes and are essential for network functionality. However, the presence of middleboxes drastically complicates the task of network verification. Previous work showed that the problem is undecidable in general and EXPSPACE-complete when abstracting away the order of packet arrival. We describe a new algorithm for conservatively checking isolation properties of stateful networks. The asymptotic complexity of the algorithm is polynomial in the size of the network, albeit being exponential in the maximal number of queries of the local state that a middlebox can do, which is often small. Our algorithm is sound, i.e., it can never miss a violation of safety but may fail to verify some properties. The algorithm performs on-the fly abstract interpretation by (1) abstracting away the order of packet processing and the number of times each packet arrives, (2) abstracting away correlations between states of different middleboxes and channel contents, and (3) representing middlebox states by their effect on each packet separately, rather than taking into account the entire state space. We show that the abstractions do not lose precision when middleboxes may reset in any state. This is encouraging since many real middleboxes reset, e.g., after some session timeout is reached or due to hardware failure

On the Complexity of an Unregulated Traffic Crossing

The steady development of motor vehicle technology will enable cars of the near future to assume an ever increasing role in the decision making and control of the vehicle itself. In the foreseeable future, cars will have the ability to communicate with one another in order to better coordinate their motion. This motivates a number of interesting algorithmic problems. One of the most challenging aspects of traffic coordination involves traffic intersections. In this paper we consider two formulations of a simple and fundamental geometric optimization problem involving coordinating the motion of vehicles through an intersection. We are given a set of $n$ vehicles in the plane, each modeled as a unit length line segment that moves monotonically, either horizontally or vertically, subject to a maximum speed limit. Each vehicle is described by a start and goal position and a start time and deadline. The question is whether, subject to the speed limit, there exists a collision-free motion plan so that each vehicle travels from its start position to its goal position prior to its deadline. We present three results. We begin by showing that this problem is NP-complete with a reduction from 3-SAT. Second, we consider a constrained version in which cars traveling horizontally can alter their speeds while cars traveling vertically cannot. We present a simple algorithm that solves this problem in $O(n \log n)$ time. Finally, we provide a solution to the discrete version of the problem and prove its asymptotic optimality in terms of the maximum delay of a vehicle

Complexity and Expressivity of Branching- and Alternating-Time Temporal Logics with Finitely Many Variables

We show that Branching-time temporal logics CTL and CTL*, as well as Alternating-time temporal logics ATL and ATL*, are as semantically expressive in the language with a single propositional variable as they are in the full language, i.e., with an unlimited supply of propositional variables. It follows that satisfiability for CTL, as well as for ATL, with a single variable is EXPTIME-complete, while satisfiability for CTL*, as well as for ATL*, with a single variable is 2EXPTIME-complete,--i.e., for these logics, the satisfiability for formulas with only one variable is as hard as satisfiability for arbitrary formulas.Comment: Prefinal version of the published pape

Should We Learn Probabilistic Models for Model Checking? A New Approach and An Empirical Study

Many automated system analysis techniques (e.g., model checking, model-based testing) rely on first obtaining a model of the system under analysis. System modeling is often done manually, which is often considered as a hindrance to adopt model-based system analysis and development techniques. To overcome this problem, researchers have proposed to automatically "learn" models based on sample system executions and shown that the learned models can be useful sometimes. There are however many questions to be answered. For instance, how much shall we generalize from the observed samples and how fast would learning converge? Or, would the analysis result based on the learned model be more accurate than the estimation we could have obtained by sampling many system executions within the same amount of time? In this work, we investigate existing algorithms for learning probabilistic models for model checking, propose an evolution-based approach for better controlling the degree of generalization and conduct an empirical study in order to answer the questions. One of our findings is that the effectiveness of learning may sometimes be limited.Comment: 15 pages, plus 2 reference pages, accepted by FASE 2017 in ETAP

Verifying Policy Enforcers

Policy enforcers are sophisticated runtime components that can prevent failures by enforcing the correct behavior of the software. While a single enforcer can be easily designed focusing only on the behavior of the application that must be monitored, the effect of multiple enforcers that enforce different policies might be hard to predict. So far, mechanisms to resolve interferences between enforcers have been based on priority mechanisms and heuristics. Although these methods provide a mechanism to take decisions when multiple enforcers try to affect the execution at a same time, they do not guarantee the lack of interference on the global behavior of the system. In this paper we present a verification strategy that can be exploited to discover interferences between sets of enforcers and thus safely identify a-priori the enforcers that can co-exist at run-time. In our evaluation, we experimented our verification method with several policy enforcers for Android and discovered some incompatibilities.Comment: Oliviero Riganelli, Daniela Micucci, Leonardo Mariani, and Yli\`es Falcone. Verifying Policy Enforcers. Proceedings of 17th International Conference on Runtime Verification (RV), 2017. (to appear

Efficient Certified RAT Verification

Clausal proofs have become a popular approach to validate the results of SAT solvers. However, validating clausal proofs in the most widely supported format (DRAT) is expensive even in highly optimized implementations. We present a new format, called LRAT, which extends the DRAT format with hints that facilitate a simple and fast validation algorithm. Checking validity of LRAT proofs can be implemented using trusted systems such as the languages supported by theorem provers. We demonstrate this by implementing two certified LRAT checkers, one in Coq and one in ACL2